Apple Music keeps turning down

I have the new iPhone 12pro max. I always use Bluetooth to listen to music via my truck radio or my shop radio. I keep the volume on my turned all the way up and then control the volume from the head unit or the shop radio but after about 10 minutes, I get an alert from sounds and hapatics stating my volume was turned down to protect my hearing. I have this feature turned off but yet it still cuts my volume to 50%. Is this a glitch in the system or did I turn it off wrong?